iwlwifi: put all the isr related function under ops

There were two type of isr supported by iwlwifi devices.
  legacy isr - only used by legacy devices (3945 & 4965)
  ict isr - used by all new generation of iwlwifi devices

Move all the isr related functions into ops, the ict type of isr
supports only needed for newer devices.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>